Recently, cars, home electric appliances, cameras, containers, etc. have been required to become lighter in weight. As such, parts in machines, appliances, etc. have been changed from metals to plastics.
Parts made of plastics consist of a plurality of molded bodies (described as first molded body or bodies in the following description), and sealing parts (described as second molded body or bodies in the following description). Sealing parts are made of such elastic polymers as silicon gum, urethane gum, styrene-butadiene gum, etc., and are used in assembling sections between parts made of plastics so as to provide sealing, absorbing or nonskid capabilities for products manufactured therewith.
Conventionally, the second molded bodies are independently molded from the first molded bodies, then they are manually assembled into the first molded bodies. In such a method, there are disadvantages of lower assembling precision and increasing assembling steps. To solve these disadvantages, there was disclosed a method of multi-injection molding in Japanese Provisional Publication (Kokai) Gazette 60-52322 and Japanese Provisional Publication (Kokai) Gazette 63-104809. The method comprises the steps of molding a first molded body having a concave section on the surface thereof by injection molding, and injecting elastic polymer for forming a second molded body in the concave section. In this conventional method, multi-injection molded bodies consisting of the first molded body and the second molded body are molded in one injection molding step, so that assembling precision can be increased, and assembling steps can be reduced.
In the above conventional method, first molded bodies are molded by injection molding, and the walls of concave sections are formed approximately vertical from the bottom faces thereof, in order that one can pick products out from molding machines easily. But in the above method, second molded bodies, molded in concave sections of first molded bodies, can also be pulled out of the first molded bodies easily because there are provided no catching means on the side wall faces of the concave sections. In order to fix second molded bodies in concave sections of first molded bodies, as disclosed in the gazett No. 63-104809, reactive elastomer layers, primer layers, etc. are formed between inner bottom faces of concave sections of first molded bodies and bottom faces of second molded bodies to adhere them.